Tube structures for heat exchanger

ABSTRACT

A fluid-carrying tube for a heat exchanger includes an outer perimeter, an inner perimeter, and a plurality of ridges extending from the inner perimeter inwardly into an interior of the tube. Each ridge includes a ridge height, a base width and a tip width. A ratio of the ridge height to the base width is between about 0.2 and about 4.0, and a ratio of the tip width to the base width is between about 0.015 and about 0.965.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to heat exchangers. Morespecifically, the subject disclosure relates to improved tube structuresfor a heat exchanger.

A simplified typical vapor compression refrigeration cycle includes anevaporator, a compressor, a condenser and an expansion device.Refrigerant flow is such that low pressure refrigerant vapor passesthrough a suction line to the compressor. The compressed refrigerantvapor is pumped to a discharge line that connects to the condenser. Aliquid line receives liquid refrigerant exiting the condenser anddirects it to the expansion device. A two-phase refrigerant is returnedto the evaporator, thereby completing the cycle.

Two of the main components in a vapor compression cycle are theevaporator and condenser heat exchangers. The most common type of heatexchanger in use is of the round tube plate fin (RTPF) constructiontype. Historically, the tubes were made of copper while the fins weretypically made of aluminum in such heat exchangers. The thermalperformance of a heat exchanger, the ability to transfer heat from onemedium to another, is inversely proportional to the sum of its thermalresistances. For a typical heating, ventilation, air conditioning andrefrigeration (HVAC&R) application using refrigerant inside the tubesand air on the external fin side, the airside thermal resistancecontributes 50-70% while refrigerant side thermal resistance is 20-40%and the metal resistance is relatively small and represents only 6-10%.Due to the continuous market pressure and regulatory requirements tomake HVAC&R units more compact and cost effective, a lot of effort hasbeen devoted to improving the heat exchanger performance on therefrigerant side as well as the airside.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a fluid-carrying tube for aheat exchanger includes an outer perimeter, an inner perimeter, and aplurality of ridges extending from the inner perimeter inwardly into aninterior of the tube. Each ridge includes a ridge height, a base widthand a tip width. A ratio of the ridge height to the base width isbetween about 0.2 and about 4.0, and a ratio of the tip width to thebase width is between about 0.015 and about 0.965.

According to another aspect of the invention, a heat exchanger includesa plurality of fins and a plurality of tubes passing a fluidtherethrough and extending through the plurality of fins. At least onetube of the plurality of tubes includes an outer perimeter, an innerperimeter, and a plurality of ridges extending from the inner perimeterinwardly into an interior of the at least one tube. Each ridge has aridge height, a base width, and a tip width. A ratio of the ridge heightto the base width is between about 0.2 and about 4.0, and a ratio of thetip width to the base width is between about 0.015 and about 0.965.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a schematic view of an embodiment of a heat exchanger;

FIG. 2 is a partial cross-sectional view of an embodiment of a heatexchanger tube; and

FIG. 3 is a cross-sectional view of an embodiment of a heat exchangertube.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

Shown in FIG. 1 is an embodiment of a round tube plate fin (RTPF) heatexchanger 10, such as one utilized as an evaporator or condenser. TheRTPF heat exchanger 10 includes a plurality of tubes 12 and a pluralityof fins 14. The plurality of tubes 12 carry a fluid, for example, arefrigerant. Thermal energy is exchanged between the fluid and airflowing past the plurality of fins 14. In some embodiments, the tubes 12may be formed of an aluminum or aluminum alloy by, for example, anextrusion process, while in other embodiments, the tubes 12 maybe formedof other materials, for example, copper, Cu—Ni, steel or plastic.

FIG. 2 illustrates a partial cross-sectional view of a tube 12 of a heatexchanger 10. The tube 12 includes a plurality of enhancements, orridges 16 extending into an interior 18 of the tube 12. As shown in FIG.3, the tube 12 has an outer perimeter 32 and an inner perimeter 34, withthe ridges 16 extending inwardly from the inner perimeter 34 into theinterior 18 of the tube 12. The ridges 16 extend along a length 20 ofthe tube 12. In some embodiments, the ridges 16 extend substantiallyaxially, while in other embodiments, the ridges 16 extend helicallyalong the tube 12 at a helix angle α with respect to a tube axis 24.Ridges 16, such as those described herein, improve the heat transfercharacteristics of the tubes 12 while maintaining a balance withpressure drop requirements to achieve a desired refrigerant flow throughthe tubes 12. Specific geometric configurations of the ridges 16,enhancing both the pre-expansion and post-expansion tube 12 surfacegeometry, are described below by way of example.

Referring again to FIG. 2, the ridges 16 have a number ofcharacteristics to define their shape and arrangement in the interior 18of the tube 12. Each ridge 16 has a ridge 16 height h, a base 26 widthw, and a tip 28 width b. Sides 30 of the ridge 16 extend from the base26 to the tip 28 at an apex angle Y. Adjacent ridges 16 are spaced by aridge 16 pitch P_(r). Each tube 12 has a tube diameter D, and a baselinetube 12 wall thickness t_(b) between adjacent ridges 16.

Shape of the ridges 16, as well as ridge 16 pitch P_(r) and a number ofridges 16 in the tube 12, N_(r), are all taken into account whencomparing an internal surface area of a tube 12 including the ridges 16to a typical tube having a smooth wall, and thus an internal diameter asshown in equation (1) of:

D−2*t _(b)   (1)

The increased internal surface area of the tube 12 including ridges 16compared to the smooth-walled tube increases the effectiveness ofthermal energy transfer between fluid in the tube 12 and an externalenvironment. The effect of the increased surface area can be expressedas an enhancement ratio R_(x) as in equation (2) below:

R _(x)=(2*h*N _(r)*((1-sin(Y/2)/(π*(D−2 *(t _(b) +h))*cos(Y/2)))+1)/cosα  (2)

As can be seen from a review of equation (2), the enhancement ratio Rxis a strong linear function of h/(π*(D−2*(t_(b)+h))/N_(r)), which is aratio of the ridge height h, to the ridge pitch P_(r).

In some embodiments, the ridges 16 may extend substantially axiallyalong the length 20, or may extend at helix angle a of between about 18degrees and about 35 degrees. Further, a ratio of the number of ridgesNr to a maximum internal diameter of the tube 12, or N_(r)/D_(imax) maybe between about 5.4 and about 10.1, where D_(imax) is specified inmillimeters. In some embodiments, a ratio of the ridge height, h, to theridge pitch, P_(r), is between about 0.17 and about 1.36. R_(x), asshown in equation 1, is between about 1.28 and about 3.49 in someembodiments, for example, those where the ridges 16 extend substantiallyaxially along the tube 12. In other embodiments, for example where thehelix angle α is not zero, R_(x) is between about 1.34 and about 4.26.In some embodiments, a ratio ridge height h to maximum internal diameterof the tube 12, or MD. , is between about 0.0008 and about 0.0870. Forsome ridges 16, the apex angle Y is between about 10 degrees and 25degrees. Further, in some embodiments, the ridge height h and base widthw are related such that a ratio of the ridge height to the base width,or h/w is between about 0.2 and about 4.0. Similarly, in otherembodiments, the tip width b and the base width w, or b/w, is betweenabout 0.015 and about 0.965.

Such ratios and ranges described above may vary for specific tube 12outer diameters. For example, for tubes 12 with outer diameters of about0.5 inches, N_(r)/D_(imax) may be between about 5.4 and about 9.25.Further, h/P_(r) is between about 0.17 and about 1.22. R_(x) is betweenabout 1.28 and about 3.23 in embodiments where the ridges 16 extendsubstantially axially along the tube 12 and where the helix angle α isnot zero, R_(x) is between about 1.34 and about 3.94. In embodiments of0.5 inch diameter tube, h/D_(imax), is between about 0.0008 and about0.035.

In other embodiments where the tubes 12 have outer diameters of about0.375 inches, N_(r)/D_(imax) , where D_(imax) is expressed inmillimeters, may be between about 5.8 and about 10.1. Further, h/P_(r)is between about 0.19 and about 1.36. R_(x) is between about 1.30 andabout 3.49 in embodiments where the ridges 16 extend substantiallyaxially along the tube 12 and where the helix angle α is not zero, R_(x)is between about 1.37 and about 4.26. In embodiments of 0.375 inchdiameter tube, h/D_(imax), is between about 0.0117 and about 0.0488.

In other embodiments where the tubes 12 have outer diameters of about 7millimeters, N_(r)/D_(imax) may be between about 5.4 and about 9.5,where D_(imax) is specified in millimeters. Further, h/P_(r) is betweenabout 0.18 and about 1.30. R_(x) is between about 1.28 and about 3.37 inembodiments where the ridges 16 extend substantially axially along thetube 12 and where the helix angle α is not zero, R_(x) is between about1.35 and about 4.12. In embodiments of 7 millimeter diameter tube,h/D_(imax), is between about 0.021 and about 0.087.

In still other embodiments where the tubes 12 have outer diameters ofabout 5 millimeters, N_(r)/D_(imax) may be between about 5.5 and about9.4, where D_(imax) is specified in millimeters. Further, h/P_(r) isbetween about 0.18 and about 1.30. R_(x) is between about 1.29 and about3.39 in embodiments where the ridges 16 extend substantially axiallyalong the tube 12 and where the helix angle a is not zero, R_(x) isbetween about 1.36 and about 4.14. In embodiments of 5 millimeterdiameter tube, h/D_(imax), is between about 0.021 and about 0.087.

While the tubes 12 illustrated herein are substantially circular, it isto be appreciated that, in other embodiments, the tubes 12 may benoncircular in cross-section having, for example, an oval, anelliptical, or a race-track cross-section. In such tubes, an equivalentto tube 12 diameter D would be a circular cross-section tube diameterthat would have identical mass or material content in the cross-sectionas the particular non-circular cross-section. All geometrical ratiosdescribed hereabove are equally applicable to such non-circular tubeconfigurations allowing achieving substantially improved in-tube thermaland hydraulic performance.

Referring to the geometric ratios described herein, tubes 12 includingsuch ridges 16 that conform to the exemplary ranges of these ratiosexhibit substantially improved thermo-hydraulic performance over priorart tubes. The ratios, and described ranges for the ratios, are notobvious and have been developed via extensive simulation andexperimentation on the component and sub-component level, whilespecifically focusing on the two-phase refrigerant flows.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. A fluid-carrying tube for a heat exchanger comprising: an outerperimeter; an inner perimeter; and a plurality of ridges extending fromthe inner perimeter inwardly into an interior of the tube, each ridgehaving; a ridge height; a base width; and a tip width; wherein a ratioof the ridge height to the base width is between about 0.2 and about4.0; and wherein a ratio of the tip width to the base width is betweenabout 0.015 and about 0.965.
 2. The tube of claim 1, wherein theplurality of ridges extend substantially axially along a length of thetube.
 3. The tube of claim 1, wherein the plurality of ridges extendhelically along a length of the tube.
 4. The tube of claim 3, wherein ahelix angle of the plurality of ridges is between about 18 degrees and35 degrees.
 5. The tube of claim 1, wherein a ratio of a number ofridges in the plurality of ridges to a maximum internal diameter of thetube expressed in millimeters is between about 5.4 and 10.1.
 6. The tubeof claim 5, wherein the ratio of a number of ridges in the plurality ofridges to a maximum internal diameter of the tube expressed inmillimeters is between about 5.5 and 9.25.
 7. The tube of claim 1,wherein a ratio of the ridge height to a ridge pitch between adjacentridges of the plurality of ridges is between about 0.17 and about 1.36.8. The tube of claim 7, wherein the ratio of the ridge height to theridge pitch is between about 0.19 and about 1.22.
 9. The tube of claim1, wherein a ratio of the ridge height to a maximum internal diameter ofthe tube is between about 0.0008 and about 0.0870.
 10. The tube of claim9, wherein the ratio of the ridge height to the maximum internaldiameter of the tube is between about 0.021 and about 0.035.
 11. Thetube of claim 1, wherein the tube is formed from an aluminum or aluminumalloy.
 12. The tube of claim 1, wherein the tube is of a substantiallynon-circular cross-section, including but not limited to oval,elliptical and race-track cross-sections.
 13. The tube of claim 1,wherein the tube has an effective diameter of between about 5millimeters and about 13 millimeters.
 14. A heat exchanger comprising: aplurality of fins; a plurality of tubes passing a fluid therethrough andextending through the plurality of fins, a least one tube of theplurality of tubes including: an outer perimeter; an inner perimeter;and a plurality of ridges extending from the inner perimeter inwardlyinto an interior of the tube, each ridge having: a ridge height; a basewidth; and a tip width; wherein a ratio of the ridge height to the basewidth is between about 0.2 and about 4.0; and wherein a ratio of the tipwidth to the base width is between about 0.015 and about 0.965.
 15. Theheat exchanger of claim 13, wherein the plurality of ridges extendsubstantially axially along a length of the at least one tube.
 16. Theheat exchanger of claim 13, wherein the plurality of ridges extendhelically along a length of the at least one tube.
 17. The heatexchanger of claim 15, wherein a helix angle of the plurality of ridgesis between about 18 degrees and 35 degrees.
 18. The heat exchanger ofclaim 13, wherein a ratio of a number of ridges in the plurality ofridges to a maximum internal diameter expressed in millimeters of the atleast one tube is between about 5.4 and 10.1.
 19. The heat exchanger ofclaim 17, wherein the ratio of a number of ridges in the plurality ofridges to a maximum internal diameter expressed in millimeters of the atleast one tube is between about 5.5 and 9.25.
 20. The heat exchanger ofclaim 13, wherein a ratio of the ridge height to a ridge pitch betweenadjacent ridges of the plurality of ridges is between about 0.17 andabout 1.36.
 21. The heat exchanger of claim 19, wherein the ratio of theridge height to the ridge pitch is between about 0.19 and about 1.22.22. The heat exchanger of claim 13, wherein a ratio of the ridge heightto a maximum internal diameter of at least one tube of the plurality oftubes is between about 0.0008 and about 0.0870.
 23. The heat exchangerof claim 13, wherein at least one tube of the plurality of tubes isformed from an aluminum or aluminum alloy.
 24. The heat exchanger ofclaim 13, wherein at least one tube of the plurality of tubes is of asubstantially non-circular cross-section, including but not limited tooval, elliptical and race-track cross-sections.
 25. The heat exchangerof claim 13, wherein at least one tube of the plurality of tubes has aneffective diameter of between about 5 millimeters and about 13millimeters.